The present invention relates to a method in a telecommunications network for use in management and/or control of a call between two transceivers. The invention relates further to an arrangement and an apparatus for use in a telecommunications network for performing call management and/or control operations.
A cellular radio telecommunication system or a Public Land mobile Network (PLMN) comprises a Mobile Services Switching Centre (MSC) for controlling and/or managing communications of a Mobile Station (MS) connected to the network system. The Mobile Station (MS) communicates with the MSC through a Base Station Subsystem (BSS), to which the MS is connected over a radio (i.e. air) interface between a Base Station (BS) of the Base Station Subsystem (BSS) and the MS. The MSC includes databases so as to enable an operation of the system. The databases are such as a Home Location Register (HLR) and a Visitor Location register (VLR) and additional databases for further subscriber information and billing operations etc.
MSCs can be divided e.g. to Visited MSCs (VMSC) and Transit MSCs (TMSC) or Gateway MSCs (GMSC). From these the VMSC is a MSC which used by a subscriber who is having a connection to a base station connected to this particular MSC. The TMSCs or the GMSCs are, in turn, used as nodes for possible routing and switching operations in the communications path between, i.e. intermediate, two VMSCs, or between a VMSC and any other exchange or switching point, or even between two TMSCs. Therefore, when a call is established between two mobile stations, the call is also accomplished between an originating VMSC and a terminating VMSC, and there may be one or several intermediate MSCs between the VMSCS.
In the mobile radio telecommunications systems or the PLMN the speech and other messaging is coded in the transmitting Mobile Station or similar transmitting and receiving terminal (transceiver), such as voice mail box, before the transmission thereof by using an appropriate coding technique. For example, in Personal Digital Cellular (PDC) system a VSELP (Vector Sum Excited Linear Prediction) 11.2 kbit/s speech coding is used on the full rate channel and a PSI-CELP (Pitch Synchronized Innovationxe2x80x94Excited Linear Prediction) 5.6 kbits/s speech coding is used on the half rate channel over an air or radio interface to the Base Station.
When having a speech call from a PLMN to a fixed network, such as to a Public Switched Telephone Network (PSTN), or to an Integrated Digital Services Network (ISDN), a transcoder or codec is connected to the originating Mobile Services Switching Centre (VMSC) controlling the radio interface between the BSS and the calling mobile station. The transcoder is used to convert the VSELP/PSI-CELP coded speech to a PCM (Pulse Code Modulation) xcexc-law coded speech so as to enable communication towards the PSTN.
When having a connection between two mobile transceiver stations, the VSELP/PSI-CELP coded speech is transmitted transparently over the PLMN network. In this instance the transcoders are through connected during the connection so as to avoid a conversion of e.g. a VSELP/PSI-CELP coded speech to a PCM xcexc-law coded speech and then back to VSELP/PSI-CELP coded speech, which would decrease the speech quality at the receiving end.
However, the transcoders are active, i.e. converting the VSELP/PSI-CELP coded speech to the PCM xcexc-law coded speech during the call setup in order to enable listening of announcements and tones from the telephone network. After the setup is completed, the transcoders are changed or switched to the through connected mode by means of a specific codec control signalling by using a Mobile Application Part (MAP) over a system 7 signalling (#SS7).
There are PLMN arrangements, such as the PDC, in which the codec control signalling occurs as end-to-end signalling, i.e. the air interface is coded from one end to the other. The messages are addressed with a Network Code (NC) and a Signalling Point Code (SPC) of the designated Visited Mobile Services Switching Centre (VMSC). The addresses are carried in an ISUP (Integrated Services Digital Network User Part) signal as an IAM (Initial Address Message).
The codec control signalling is performed for basic calls only according to a DMNI (Digital Mobile Communications Network Internode Interface) standard. For example, at forwarded calls the codec control is not performed, but the PCM xcexc-law speech coding is always used between the originating VMSC and the terminating VMSC. This, however, causes a remarkable decrease in speech quality.
Since the codec control signalling occurs as an end-to-end signalling, the intermediate nodes or connection points, like transit exchanges or MSCs or Service Switching Points (SSP) providing Intelligent Network (IN) services, are not able to know the speech coding used in the communications. This is a disadvantage e.g. in cases where monitoring equipment or similar, or an announcement should be connected to the call. As the coding in use is not exactly known, the system is not aware of the coding by which announces, messages, information, tones etc. should be transmitted to the mobile station(s) or which coding should be used to decode received announces, tones, control messages etc. In addition, it is not possible to affect and control the used coding during the connection (e.g. it is not possible to change the mode of the coding e.g. from VSELP to xcexc-law coding during the call), which might be required e.g. in cases where a conference call with a third party should be set up during an already existing call between two parties. In case this information is to be transmitted separately from the terminating (or originating) VMSC to the intermediate node later on during or after the setup, a separate and additional messaging arrangement for this is needed.
It is an object of the present invention to overcome the disadvantages of the prior art solutions and to provide a new type of solution for controlling and/or managing a call using end to end signalling.
An object of the present invention is to provide a solution by means of which the management and monitoring of calls is made easier to accomplish in the intermediate nodes of a Land Mobile Network.
An object of the present invention is to provide a solution by means of which unnecessary coding/decoding in a call between two transceivers communicating through a cellular system is avoided.
An object of the present invention is to provide a solution by means of which a delay and/or additional signalling in switching additional features and/or services to a call implemented by means of end-to-end signalling is avoided.
An object of the present invention is to provide a solution in which speech quality of a call between two mobile stations is improved.
An object of the present invention is to provide a solution by means of which switching operations, such as switching a call to Intelligent Network service applications or switching of monitoring apparatus or announcements to a call, can be eased.
The objects are obtained by a method of implementing a call in a telecommunications system, the call being routed from a first transceiver to a second transceiver via a first switching centre and a second subsequent switching centre, the method comprising:
including in a call setup message from the first switching centre to the second switching centre an address of said first switching centre;
intercepting the call setup message at a telecommunications node intermediate to the first and second switching centres;
replacing the address of the first switching centre in the setup message from the first switching centre with an address of the intermediate node;
forwarding the call set up message transmission to the second switching centre; and
sending a response message including call set up information and using end to end signalling from said second switching centre, said response message using said substitute address of the intermediate node and being terminated in the intermediate node.
An embodiment of the invention provides an arrangement in a telecommunications system, said arrangement comprising:
a first transceiver,
a second transceiver,
a first switching centre through which the first transceiver may communicate and which has a first address,
a second switching centre through which the second transceiver may communicate and which has a second address, a communication path between the first switching centre and the subsequent second switching centre,
an intermediate node in the communication path between said first switching centre and said second switching centre, a call from the first transceiver to the second transceiver being routed through said intermediate node,
wherein the arrangement is such that the intermediate node is arranged to intercept the address the first switching centre included in a setup message of the call, and to replace said address with an address of the intermediate node, whereby responding messages using end to end signalling from the second switching centre concerning the call are addressed to the intermediate node.
According to an embodiment an intermediate switching centre for use in a communication path between a first switching centre and a subsequent second switching centre of telecommunications system is provided, wherein a call from a first transceiver to a second transceiver is routed through said intermediate switching centre, and wherein the intermediate switching centre is arranged to intercept and replace an address of the first switching centre contained in a setup message of the call with a new address, whereby response messages implemented by means of end to end signalling from the second switching centre are addressed to a destination designated by said new address.
Several advantages are obtained by means of the present invention, since the solution provides a simple and reliable manner for call management and control. The solution enables monitoring of calls using end to end signalling (e.g. calls from a mobile station to another mobile station or transceiver in a PDC system) in intermediate nodes, such as transit MSCs. The solution enables further a change of a transcoder mode by the intermediate nodes for supporting services provided by an intelligent network (IN). In addition, delays in the signalling and amount of undesired signalling can be decreased, and the quality of calls from a mobile station to another mobile station call can be improved.
In the following the present invention and the other objects and advantages thereof will be described in an exemplifying manner with reference to the annexed drawings, in which similar reference characters throughout the various figures refer to similar features.